Removal of oxygen from metals



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. 1? 50 REMOVALoFoXYGE -FR M META S it Bertrain C." Raylies Merle SiberQEuclid, Ohio,

assignors, by mesne assignment's, to Horizons'Titanium Corporation, Princeton" Jersey No Drawing. Application April 26, 1954, Serial No. 425,768

2 Claims. '(Cl. 204-140) This invention relates to the purification of certain metals and, more particularly, to the removal of oxygen present as an impurity in certain'metals havinga pronounced afiinity for oxygen. There are a number of metals which not only have a titanium metal will produce a threefold increase in the hardness of the metal, an'increase so great as to render the metal unworkable on a commercial scale. In the case of titanium and zirconium,' fl1e presently available For example, the presence of e be the simple halides or the complex halides such"as double fluorides of the metal and an alkali metal.

The cells in which this electrolytic purification ma be performed by the practic'e of 'ou'r' invention comprise" any of the conventional 'cell designs' which have been found usefulheretofore. When the electrolyte comprises a mfpbmfion of Y i one or more salts maintained inthe fused state, the cell should of course be of conventional closed design so as to permit the maintenance of an inert cell atmosphere to prevent contamination of the bath;'a'nd hence the metal,

with oxygen or nitrogen from atmospheric air 'or moisture.

The oxygen-containing metal whichis to bejpurified by the method of our invention may be present in' the electrolyte 'in any physicalform ranging from finely divided metalto large and coherent masses of the metal. The

' finely divided metal may be made anodic simply by charging it into the bath andby permitting it torest on the bottom ofthebath container' which also serves as the anode for the cell or by maintaining it within the confines of an anodically connected porous barrier surll rounding the cell anode. Massive pieces of the oxygenmethods for producing these metals tend to yield the metal in ingot form with a larger percentage of contained oxygen than is compatible with optimum mechanical properties for the metal. To the best of 'our present knowledge, there is no available procedure for removing this contained oxygen from titanium metal, although its oxygen content can be lowered somewhat by blending the oxygen-containing titanium with substantially oxygenfree titanium. p 1 r We havenow discovered that it is possible to remove by electrolytic means at least a major portion of the oxygen content of metals of the type in which oxygen dissolves interstitially. More specifically, we have found that when these oxygen-containing metals are made anodic in an electrolytic cell and when the anode voltage is sufficiently low to prevent anodic oxidation of the metal, the oxygen component of the metal can be caused to be transported through the bath and be deposited on the cathode. This discovery is applicable, we have found, to the removal of oxygen from titanium and zirconium. The method of our invention for removing oxygen from these metals comprises anodically electrolyzing the oxygen-containing metal at a voltage below that at which the anodic metal is electrolytically oxidized in an electrolyte containing carrier ions of the metals, continuing the electrolysis until a substantial portion of the oxygen content of the anodic metal has been transported to the cathode, and has thereby been removed from the anodic metal, and recovering the resulting deoxidized anodic metal.

The electrolytes in which the deoxidation of the aforementioned metals is effected pursuant to our invention may be a fused salt electrolyte. The electrolyte should contain carrier ions of the metal which is to be deoxidized by the method of the invention. For example, useful fused salt baths may be made up of alkali metal halides or alkaline earth metal halides or mixtures of such halidesf The choice of metal and halide components for such a bath has no apparent effect upon the operability of our method, the choice of bath components being predicated primarily upon the melting point and volatility of the fused bath. Any of the halides of the metal to be oxidized may be used as the source of carrier ions in the fused salt bath, and these halides may containing metal may be similarly charged into the bath; or maybe used directly as thebath. anode. Regardless,

of. the form'in which the oxygen-containing metal is present in contact with the electrolyte t must be made anodic, by suitable electrical connec tio y ,.The anode voltage which is used in practicingoufinvention should be suflicientlyllowf to prevent anodic oxidation of the metal. In general, the an'od e voltage,should be less than about 2 *volts' and voltagesjless than aboutl volt are generally satisfactory. I It must be understood, however, that the anode voltagelimit depends upon the metal itself and upon the electrolyte composition, the only requirement being that the anode 'voltage islow enough to prevent anodic foxidation of the metal to bepurified. Within these prescribed conditions, theoxyg'encomponent of the anodic metal is transported through the electrolyte and is deposited on the cathode, generally in the form of a high oxygen-content form of the anodic metal. The metal component of the anodic oxygen-containing metal is largely unaffected by this electrolysis and remains in its original, form except for the depletion of its oxygen content. After electrolysis has proceeded for a sufficient period of time to transport a significant proportion of the oxygen component of the anodic metal to the cathode, it will be found that the anodic metal residue comprises high purity metal largely freed of its initial oxygen impurity.

The following examples are illustrative of the practice of our invention:

Example I A mixture of 4 parts of sodium chloride and /2 part by weight of potassium fiuotitanate (KzTiFs) was fused in a graphite crucible enclosed in a vessel in which an inert atmosphere of argon was maintained. The graphite crucible served as the anode of an electrolytic cell, the cathode being a graphite electrode inserted into the center of the fused salt bath. About parts by weight of titanium metal containing about 0.5% oxygen by weight and having a Brinell hardness number of 220 were added to the fused salt bath wherein the titanium sank to the bottom and rested in electrical contact with the graphite crucible anode. An electrolyzing voltage of 2 volts was applied across the anode and catohde, and electrolysis was continued at this voltage while maintaining the bath temperature at about 800 C. for a period of one hour. Electrolysis was then discontinued and the The resulting solidified bath was removed en masse from the crucible and this mass was then separated from the centrally positioned cathode, Asmalldeposit of. titanium metal very high in oxygen was deposited on the cathode. Substantially all of the added titanium metal remained inithe metallic state and was separated from the solidified bath by grinding and leaching of :the 'saltrcomponents.

The titanium .metal thus recovered from :the salt bath was..-arc melted in aninert atmosphere by conventional. The resulting titanium-billet was found to:

procedure. have an oxygen content of about 0.1% and had a Brinell. hardness number of about'litl,

- I I Example 11 7 Into a bath identical with that described in Example I there were inserted both a graphite cathode and an anode of sintered titanium sponge having an oxygen content of about 0.5% by weight. and a Bri-nell hardness .number of about 220. The fused salt'bath was maintained at a temperature of about 800 C., and electrolysis wascan ried out for'onehouratflLS volts. The titanium anode was then ,withdrawnfrom the fused salt bath and was cooled in' an argon atmosphere The oxygen content of the thus;treated titanium metal was found tobe about 0.1% and its Br'inell hardness number was about 150.

.7 Example III 7 V :Amixture or 31 parts of sodium chloride and 1 parts by weight of potassium fluozirconate (KzZl'Fs) was meltedtona cruciblef and cell such as that described in Example I. Both "offthe reagents were substantially oxide-free and were anhydrous. 'Electrolysis was car-- rie dout between" a graphitekathodeand a tubular 'zir:

oxygen and had a Brinell hardness number of 210.

Electrolysis was continued at a voltage slight less than: 2 volts for 90"minutes, and after, theelectrolysis was" terminated the anode was withdrawn fromthe fused bath and was cooled in an argon atmosphere. The oxygen content of the resulting zirconium metal anode 'Was 0.07% by weight a'ndfits Brinnell hardness number was 145. I

It will be appreciated, accordingly, that the method of our invention makes it possible to remove by electrolytic means the small oxygen contentin the aforementioned transition metals so as to reduce their hardness to the rier ions of said metal, continuing the, electrolysis until a substantial portion of the oxygen content of the anodic' metal has been transported to the cathode and has thereby been removed from the anodic metal, and recovering the resulting deoxidiz'e'd anodic metal.

2. The method of removing oxygen from oxygen-contaming metals of the group consisting of titanium and zirconium which compriseselectrolyzing said oxygen-com taining metal as the anode at a voltage below that at. which the anodic metal is electrolytically oxidized in a fused electrolyte containing carrier ions of said metal,

' conium metal anode both insertedflin the fused salt bath.

The zirconium metal contained about 0.7% by weight of" continuing the electrolysis until a substantial portion of. thefloxygenrconten't of the anodic metal has been transported tothecathode and has thereby been removed from the :anodic metal, and recovering the resulting deoxidized anodic ,metal. 1

References Cited in the file of this patent UN-lTED STAT-ES PATENTS ,933,319

Driggs et'al Oct. 31, 1933 FOREIGN PATENTS 554,829 Great Britain July 21, 1943 

1. THE METHOD OF REMOVING OXYGEN FROM OXYGEN-CONTAINING METALS OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WHICH COMPRISES ANODICALLY ELECTROLYZING SAID OXYGEN-CONTAINING METAL AT A CELL VOLTAGE BELOW ABOUT 2 VOLTS IN A FUSED HALIDE SALT ELECTROLYTE CONTAINING CARRIER IONS OF SAID METAL, CONTINUING THE ELECTROLYSIS UNTIL A SUBSTANTIAL PORTION OF THE OXYGEN CONTENT OF THE ANODIC METAL HAS BEEN TRANSPORTED TO THE CATHODE AND HAS THEREBY BEEN REMOVED FROM THE ANODIC METAL, AND RECOVERING THE RESULTING DEOXIDIZED ANODIC METAL. 